1. Field of the Invention
The invention relates to a filtering device or screen which can be incorporated at any desired location in a tubular drill string for the purpose of filtering debris out of the drilling fluid and which can be conveniently removed either manually when the screen is adjacent the rig floor, or removed by an overshot type fishing tool when the screen is positioned downhole.
2. History of the Prior Art
In the drilling of subterranean wells it is very desirable to filter the drilling fluid so that it does not contain any solids that may plug or damage any of the downhole tools. It therefore has been the common practice to install a filter at the mud pump, but this filter has often proved inadequate and also provides no protection for debris that may be accidentally dropped into the tubular drill string in the process of its assemblage on the rig floor. To alleviate this condition, mud screens have been inserted into the tubular drill string but have had the disadvantage of being cumbersome to install and even more difficult to remove or to clean, if necessary. In most cases, the removal can only be accomplished by tripping the pipe out of the hole which, of course, becomes impossible in the event that the pipe is stuck. If left in place, the downhole screen will provide a blockage to any tools such as survey instruments, string shots, etc. that may be desired to be run any time during the drilling operation. Of course, the screen may eventually become plugged and severely limit the flow of fluid unless it is removed and cleaned occasionally. Downhole type screens heretofore provided have not been capable of removal without running an extreme risk that the debris that the debris that has been captured by the screen will escape from the screen during the removal process and plug the downhole devices that were meant to be protected in the first place.